The US is withholding some $800 million in aid to Pakistan, almost a third of the $2.7bn in security assistance it provides each year to the South Asian nation, Barack Obama’s chief of staff has confirmed. Relations between the key allies, always tricky, have drastically deteriorated since US commandos shot and killed al-Qaeda leader Osama bin Laden on May 2 in a Pakistani garrison town, sowing distrust on both sides. Last month, Hillary Clinton, the secretary of state,